Sometimes the drugs don’t work. Roche damped any festive cheer Friday with negative trial data that sent its shares down 5%.

The failure of one Alzheimer’s drug shouldn’t have rattled investors. But disappointment across the board in a breast cancer study, which failed to establish that new drug Kadcyla worked better than current treatments, will hit growth forecasts for the Swiss company’s prized oncology business.

The big hope for Kadcyla was that it would prove superior to other treatments when used earlier in the disease and with Roche’s other drug Perjeta. That raised the prospect of using two expensive drugs in combination for longer, boosting sales.

In reality, that outcome wasn’t likely, not least because of mounting pressure on drug prices globally. And Roche’s Herceptin and Perjeta remain the benchmark for breast cancer care after strong trial data earlier this year. But Friday’s news will still remove about 1 billion Swiss francs ($1 billion) from 2020 sales forecasts, reckons Morgan Stanley, or 3 to 4% off earnings per share.

More broadly, the disappointment is likely to heighten worries that Roche’s oncology business is vulnerable to competition. Proving Kadcyla’s superiority to Herceptin, Roche’s older drug with about 6 billion francs a year in sales, could have helped insulate those revenues from potential copycat rivals. That remains as a lingering risk.

Angst over biosimilar competition for Roche isn't a terrible problem to have. It reflects the fact that the company’s business is defensive; comprised of complex, biologic drugs that are difficult to copy. Sales of these products don’t evaporate as soon as their patent protection ends, as with easily-copied pills. In any case, there are, as yet, no imitations of Herceptin filed with regulators, still less on the market. Potential copies in the works appear to be delayed.

And Roche, as usual, does have more in its pipeline to offer investors. The focus next year will be on trials of a new multiple sclerosis drug; there is still much excitement over immuno-oncology treatments, where Roche is among the leading contenders in developing drugs that harness the body’s immune system to fight cancer.

After a somewhat lackluster 2014, Roche is trading roughly in line with the global pharmaceutical sector on a price-earnings basis, where it has generally commanded a premium. Next year, it still needs to find a pick-me-up.